In injection foam molding performed by an injection molding machine, for the purposes of obtaining a light and durable molded product with a good appearance, a top surface is cured and then its interior is foamed. To achieve this, there is conventionally known an injection foam molding method in which a foamable resin that is plasticized by heating is injected and filled within a mold at high speed, the top surface of the molded product contacting the mold is cooled and cured after completion of injecting and filling, and thereafter, the volume of a mold cavity is enlarged by widening a mold interval to decrease an internal pressure of the molded product, thereby foaming and expanding the interior of the molded product.
A foamable-resin molding device is described with reference to a conventional example in Patent Document 1. In this molding device, a hydraulic cylinder different from a clamping hydraulic cylinder is provided on a fixed board to widen a mold interval, and after the top surface of a molded product is cooled and cured, the hydraulic cylinder is activated from a state that the mold is closely adhered, thereby widening the mold interval by a foaming and expanding amount of a resin. This molding device includes a unit that adjusts a stroke of the hydraulic cylinder and a unit that precisely sets a leading-end position of a protruding rod fixed on a movable board abutted to an activating rod end of the hydraulic cylinder.
According to a foamable-resin molding device in a conventional example described in Patent Document 2, it is molded such that in a foam-molding injection molding machine in which after a resin mixed with a foaming agent is injected in a cavity formed between a fixed mold provided on a fixed board and a movable mold provided on a movable board, the movable mold is moved by a predetermined distance in a mold-opening direction in response to foaming of the resin that is mixed with a foaming agent, a movable mold-moving mechanism that can be abutted to and be spaced from an alternate one of the movable platen and the fixed board by using a servo motor and a screw is provided at one of the movable platen and the fixed platen. An object of this molding device is to obtain a high-quality foam-molded product by highly accurately controlling the speed when moving the movable mold in a mold-opening direction and its stop position in response to foaming of the resin that is mixed with a foaming agent.
In a foamable-resin molding device in a conventional example described in Patent Document 3, when foaming a molten resin injected and filled in a mold cavity by slightly opening a mold, slight-opening speed is controlled such that an in-mold pressure detected by an in-mold pressure sensor does not reach a minus value, drive of slightly opening a mold during foaming employs a plurality of ball screw type jacks, and a servo motor that drives the jacks is tuning-controlled, thereby making the thickness of molded products even.
Patent Document 1: Japanese Patent Application Publication No. S52-25429 (FIGS. 1 and 3)
Patent Document 2: Japanese Patent Application Laid-open No. 2002-321262 (FIG. 4)
Patent Document 3: Japanese Patent Application Laid-open No. 2004-98582 (FIG. 1)